1. Field of the Invention
The present invention relates to a fuel injection control system of an internal combustion engine.
2. Description of Related Art
A fuel injection control system of an internal combustion engine regulates opening timing and closing timing of injectors, which specify fuel injection timing and a fuel injection quantity. A control section of the fuel injection control system sets the injection timing and the injection quantity so that desired torque is generated and good gas mileage is achieved, based on a result of measurement of an operating state of the engine. A fuel injection control system of a compression ignition type internal combustion engine disclosed in Unexamined Japanese Patent Application Publication No. S61-234246 (Patent Document 1) or No. S62-32247 (Patent Document 2) measures ignition timing as the operating state and feedback-controls the fuel injection timing so that the ignition timing coincides with predetermined target timing. Thus, heat efficiency and the gas mileage can be improved. The technology disclosed in Patent Document 2 stops the feedback control to prevent abnormal advancement of the ignition timing if the operating state is a certain state in which large variations are generated in the ignition timing measurement.
A fuel injection control system disclosed in Unexamined Japanese Petty Patent Application Publication No. S58-165229 (Patent Document 3) or Unexamined Japanese Patent Application Publication No. 2002-180879 (Patent Document 4) measures a cylinder pressure as the operating state and feedback-controls the fuel injection timing so that a maximum value of the cylinder pressure does not exceed a predetermined upper limit value. Thus, the engine can be protected from an excessive increase of the cylinder pressure.
The technology disclosed in Patent Document 1 or Patent Document 2 feedback-controls the fuel injection timing not for protecting the engine but for improving the gas mileage. The technology disclosed in Patent Document 3 or Patent Document 4 feedback-controls the fuel injection timing not for improving the gas mileage but for protecting the engine. More specifically, if the improvement of the gas mileage is maximized, there is a possibility that the engine is damaged. If the protection of the engine is maximized, there is a possibility that the gas mileage is not improved sufficiently. The technology disclosed in Patent Document 2 merely prohibits the improper feedback control when the measurement accuracy of the operating state of the engine is insufficient. This technology does not aim to achieve the improvement of the gas mileage and the protection of the engine at the same time.